1. Field of the Invention
The invention relates to the treatment of household and industrial sewage with the content of organic impurities in BOD making 50 to 50,000 mg/dm3, suspended matters from 50 to 1,500 mg/dm3, fats up to 300 mg/dm3, which can be used for the purification of the waste water produced by dwelling-houses, villages, towns and cities, meat-packing plants, fish processing plants, canneries, cattle breeding farms, yeast factories, breweries, sugar-mills, pulp and paper mills, chemical and microbiological enterprises, etc. The invention is also designed to purify sewage with a high content of hydrosulfides and sulphuretted hydrogen (5 to 100 mg/dm3), ammonia nitrogen (50 to 100 mg/dm3) due to the decay of the organic impurities in the collectors and receivers of transfer pumping stations, receipt of detritus pit and cesspool sewage, as well as methane fermentation of anaerobic digesters.
2. The Prior Art
Known is an activated sludge treatment plant consisting of a biofilter located above the air-tank separator with delivery pipes for liquid jet aeration, attached to the biofilter collecting tray, a mixing chamber and a circulation pump (USSR Certificate of Authorship No. 1020379, MKI SO2 F3/02 publ. May 30, 1983). The device functions as follows: the sewage, after pretreatment (particulate pollutants removed), is driven to the mixing chamber together with the sludge mixture driven by hydrostatic head from the air-tank separator. Then the sewage-and-sludge mixture is circulated by the pump through the biofilter, delivery pipes (aeratic columns), and air-tank separator. The impurities are biologically oxidized by the biocenosis attached to the biofilter feed and active sludge microorganisms in the air-tank separator. When irrigated and driven through the biofilter, the sludge mixture is saturated with aerial oxygen. Additional saturation of the liquid with oxygen in the aeration tank and its content interfusion is due to the air-entraining of the delivery pipes (aeration columns), gas-liquid flow movement and air bubble floating. The advantages of this plant are: high sewage purification level due to the combination of the oxidative and better characteristics of the biofilter biocenosis and the aeration tank active sludge microflora; application, as a basic device, of a simple low pressure pump, and low power consumption (up to 0.5 kWt per a kilo of removed BOD). The biofilters blow away sulphuretted hydrogen and sorb hydrosulfides with the adapted sludge, which promotes effective purification of sewage with a high content of the said compounds. At the same time application of a single combined plant being a single unit is irrational for sewage treatment within the capacity range between 100 and 50,000 m3/day since the hydrodynamical mode control of the plant becomes more complicated and a repair shutdown of some elements is impossible.
The biofilter's specific weight in the general purification effect of the combined plant may be raised and correspondingly the power consumption cut through a constructive design of the biofilter having a feed of spherically shaped ceramic elements with surface cavities (RF Patent No. 2310499 BO1D 53/18 publ. Nov. 20, 2007) developed for chemical mass-transfer apparatuses.
Known also is a strong sewage biochemical treatment plant, RF Patent No. 2139257, MKI SO2 F3/02, publ. Oct. 10, 1999, whose aeration tank and bioreactor are equipped with biological feed blocks of sheets provided with holes and bristles permitting to raise the gross amount of the active biomass, nitrifiers included.
The most similar by its critical limitations (prototype) to the claimed invention is the sewage biochemical treatment plant described in RF Patent No. 2220915, MKI SO2 F3/02, publ. Oct. 10, 2004. The combined plant biofilter irrigation evenness depends not just on the lock valves where the sewage-and-sludge mixture is driven to the trays, but also on the availability of the pressure reducing devices as the liquid is driven to the trays, because of the abrupt liquid wave motion at the initial sections. The biofilter feed irrigation evenness at a minimum consumption of power for driving the liquid to the irrigation system depends on both the level of the upper cuts at the emptying fittings to the reflective disks (1 to 1.5 m) and the distances between the trays and the distances between the emptying fittings. The dimensions of the emptying fittings (4 to 10 diameters) shown in this Patent provide density of the falling liquid jets and diversity of the liquid drops reflection pathways. At the same time, as there appears a layer of attached microflora on the inside surface of the fittings (β≈1.5 mm), the fittings diameter making 20 to 35 mm and their length exceeding 6 diameters, as well as due to the claws, abruptly falls the fittings' delivery capacity and raises their obstruction probability, which demands frequent cleaning.
The efficiency of the organic impurities oxidation in the combined plant biofilters depends on the feed design. A flat feed is blocks of corrugated sheets of various coarseness, which facilitates biomass growth in the feed upper section and excludes silting in the middle and lower sections.
However application of man-made dielectric materials like fiberglass, ceramoplastic, plastics, fails to provide sufficient clutch between the microflora and the feed surface. The manufacturing testing has shown that the best clutch between the biomass and the feed surface is performed by ceramics.
The combined plant water-jet aeration unit provides efficient saturation of liquid with oxygen and stirring of the aeration tank contents only in case of the aeration columns definite diameters and definite proportions between the columns height above the surface and the height of the sunk sections of the columns. A correct choice of parameters minimizes power consumption for sewage treatment. The efficiency of air-entraining in the columns is influenced by the conditions under which the sewage-and-sludge mixture gets to the sewage collectors, the horizontal distances between the upper cuts of the aeration columns, and the precision of fixing the upper cuts of the aeration columns in relation to the water level. The heliciform claws in the upper sections of the columns raise the clogging ability of the columns in case of long-fibered impurities. The prototype sewage biochemical treatment plant presupposes that to stir the aeration tank contents the pipes lower ends are evenly placed above the flat section of the aeration tank bottom at a distance of 0.2 to 0.3 m from it.
At the same time prevention of sludge deposition and decay with a minimum power consumption for the sludge mixture circulation, keeping the active biomass of the aeration zone in a suspended state, depend on both the aeration columns diameter, the admission charge (m3/h) and the proportion of the aeration columns heights above and under the liquid level, as well as on the distances between the upper and lower columns cuts, distances between the columns ends and the angle of coupling between the flat and conic sections of the bottom and the even sludge diversion.
The sewage settlings optimally contain carbon, nitrogen, phosphorus and trace elements. However any possibility of using settlings as a fertilizer is restricted due to the vital capacity of helminths and odor nuisances as these are introduced into soil. Application of microwave frequency installations dehelmintizes the settlings completely. The excess sludge removed from the combined plants, is characterized by an optimal proportion of its biogenic elements, fine water yielding capacity and high mineralisation. Absence of primary settlers within the combined treatment plant flow schemes, aeration tanks and secondary settlers blocking excludes settlings deposition and decay and correspondingly any odor nuisances, unlike traditional plants whose settlings retain putrefactive ferments. That is why the excess sludge can be used as a fertilizer.
The major impacts on the biological sewage treatment are initial sewage and open air temperatures. The average cold weather sewage temperature in the towns and cities of Russia is between 15 and 17° C., while that in medium and small villages is 9 to 14° C. Within average aeration mode tanks, if air the temperature is minus 10 to 20° C., the liquid temperatures falls during treatment by 1 to 3° C., and within extended mode aeration tanks it falls by 4 to 9° C., which results in biological treatment deceleration or complete cessation. In the hot countries, high sewage and air temperatures, as well as direct sunlight, raise the treated liquid up to 35° C. and more, which also adversely effects air solubility and treatment speed. A closed design for sewage treatment plants partially solves the problem of liquid cooling or heating, yet the basic line of optimization of the plant's temperature mode and reduction of power consumption for air treatment is to raise the air oxygen use factor.
As the sewage is purified in the aeration tanks, there is a large number of bubbles that burst and thus form drops getting up to the atmosphere and carrying pathogenic microflora with themselves. This way the air is polluted with infectious and invasion diseases agents. To disinfect and deodorize the technological air, the plants are to be provided with air treatment devices. The three and four-stage air treatment schemes of the plants installed in the cities of Monaco, Nice, Antibes use wet hypochlorite, caustic soda treatment, and all fetid odors are removed with ozone, which makes air purification too expensive.
The objective as viewed by the designers of the new sewage biochemical treatment plant was to create such variants that would provide efficient and steady quality of treatment of sewage characterized by low and high organic impurities concentrations, high content of sulphuretted hydrogen and hydrosulfides, ammonium nitrogen, and raise the environmental safety of the purified sewage, particularly reduce the sanitary protection zone around the plant.
The solution of the designers' task resulted in technical terms in the raise of the plant's performance and stability of work at various concentrations of the impurities. Better performance and stability of work predetermined lower power consumption for sewage treatment, disinfection and used air deodorization. Above all, the plant enabled to utilize the waste producing granulated fertilizers.